1. Field of the Invention
The present invention relates to a projection display apparatus such as a projector, etc., and a display control method thereof, and more particularly relates to a projection display apparatus for projecting a color image on a screen in expansion and a display control method thereof.
2. Description of the Related Art
The colors we see everyday are categorized into two types, namely, the colors of objects (object colors) expressed by pigments, paints, etc., and the colors of light (illuminant colors) expressed by light's three primary colors on a display screen such as a projection display apparatus, a television receiver, a personal computer display, etc.
One of the differences between the object colors and the illuminant colors is the combinations of the primary colors. The primary colors of the object colors are the three of magenta (abbreviated as M), yellow (abbreviated as Y), and cyan (abbreviated as C). As compared with this, the primary colors of the illuminant colors are the three of blue (abbreviated as B), green (abbreviated as G), and red (abbreviated as R). Though blue among the primary colors of the illuminant colors is not strictly pure blue but violet-blue, this will be called “blue” throughout herein for easier understanding. That is, the three primary colors of the illuminant colors are “red (R)”, “green (G)”, and “blue (B)”.
Another difference between the object colors and the illuminant colors is how the colors appear when the primary colors are mixed (color blending effects). That is, in case of the object colors, since more light is absorbed as more colors are blended, the amount of light reflected reduces subtractively, gradually making the color subdued. This is called subtractive color mixing. In contrast, in case of the illuminant colors, color blending directly leads to an increase of the amount of light, making the color more and more vivid. This is called additive color mixing.
A display apparatus such as a projection display apparatus makes up a display image with multiple pixels constituted by dots of the light's three primary colors. The display apparatus expresses various colors by increasing or reducing the brightness of each dot while utilizing the above-described “additive color mixing”.
While one senses the colors subjectively, the colors can be represented by three measures of hue, brightness, and saturation. These are called three attributes of color. The hue indicates the differences in colors, i.e., the same things as we daily perceive or name as “colors” such as red, green, blue, etc. The brightness indicates the brilliance of colors. The brightest color is white and the darkest color is black. The saturation is how the color is vivid. As the saturation lowers, the color becomes subdued and colorless, while as the saturation increases, the color becomes garish.
FIG. 29 is a CIE chromaticity diagram (particularly, a CIE xy chromaticity diagram taking x and y coordinate axes) established by the International Commission on Illumination (CIE). This chromaticity diagram represents the schematized three attributes of color, where the broken line shaped like a sail of a yacht is the trajectory of the visible light spectrum (from about 380 nm to 780 nm). All existing colors can be distributed within this spectrum trajectory. The trajectory has some black dots for expediency, with the values besides the black dots indicating the wavelength (420 nm, 480 nm, . . . , 700 nm) of the colors on the x-y coordinates. These values have no particular meaning, but are merely indicated as examples.
The triangle drawn within the spectrum trajectory is the range in which a color CRT (Cathode Ray Tube) reproduces colors. As the area of the triangle increases, more colors can be reproduced. The vertices of the triangle represents the chromatic coordinates of red (R), green (G), and blue (B). The “W” positioned almost at the center of the triangle represents the standard illuminant color (white). Colors closer to W have lower “chromaticity”. The “chromaticity” means the color, which is independent from the brightness among the elements we consider to be associated with colors. In many cases, the chromaticity is divided into “hue” and “saturation”.
As obvious from the above, the CIE xy chromaticity diagram can represent the chromaticity, i.e., “hue” and “saturation” of all the colors by x-y coordinates. The “brightness” among the three attributes of colors can be represented by another axis (z axis). That is, this CIE xy chromaticity diagram shows one cross-sectional surface of a three-dimensional figure extending in the back and forth direction of the drawing, as sliced along a direction perpendicular to the z axis, which means that the position at which the z axis is perpendicularly crossed, i.e., at which the slicing takes place, represents the brightness. The origin on the z axis represents zero brightness, and the dynamic range of the brightness broadens as the three-dimensional figure gets higher.
With such basic knowledge about color informed, a conventional projection display apparatus (hereinafter referred to as conventional apparatus) will be explained (for example, see Unexamined Japanese Patent Application KOKAI Publication No. 2004-45989).
FIG. 30A is a structure diagram of a color wheel used in the conventional apparatus. The color wheel is an optical device for dividing a white light into the light's three primary colors on the temporal axis. While the basic color wheel has three areas corresponding to RGB, a color wheel that has a transmission area for a white light (W) in addition to the RGB areas is shown here. That is, the illustrated color wheel 1 is constituted by a glass disk in which a motor shaft attaching portion 2 is opened at the center, and which is radially quadrisected by 90 degrees each to provide a red spectrum area (R area 1a), a green spectrum area (G area 1b), a blue spectrum area (B area 1c), and a white light transmission area (W area 1d).
The color wheel 1 is rotatably driven by an unillustrated motor. While the color wheel 1 is rotated, a white spotlight 3 from an unillustrated light source is irradiated on an arbitrary portion on a concentric circle of the color wheel 1.
The size of the spotlight 3 is sufficiently smaller than the size of the R area 1a, the G area 1b, the B area 1c, and the W area 1d. Therefore, with the rotational direction of the color wheel 1 assumed as the counterclockwise direction with respect to the drawing, when the spotlight 3 is irradiated on the R area 1a, a red light is emitted from the color wheel 1. When the spotlight 3 is irradiated on the G area 1b, a green light is emitted from the color wheel 1. When the spotlight 3 is irradiated on the B area 1c, a blue light is emitted from the color wheel 1. Further, when the spotlight 3 is irradiated on the W area 1d, a white light is emitted from the color wheel 1.
FIGS. 30B to D show how the spotlight 3 goes across a boundary 4 between the areas (hereinafter referred to as transboundary state). As will be explained in detail later, in this transboundary state, the spotlight 3 shifts from a state as shown in FIG. 30B where it is irradiated on a single area (the R area 1a in the drawing), undergoes a state as shown in FIG. 30C where it straddles over two areas (the R area 1a and the G area 1b in the drawing), and reaches a state as shown in FIG. 30D where it again is irradiated on a signal area (the G area 1b in the drawing), as the color wheel 1 is rotated.
Thus, in the transboundary state, color mixing is obtained between the two spectrum areas (the R area 1a and the G area 1b in the drawing, also called segment) that adjoin the boundary 4. The ratio of color mixing changes in accordance with the distribution of the area of the spotlight 3 between the respective areas onto which the spotlight 3 is irradiated. That is, as the state shifts from FIG. 30B (first spectrum area, provisionally) to FIG. 30C (second spectrum area, provisionally), the ratio of green included in red gradually increases, making the initially red color yellowish stepwise. Then, the ratio of red and green is balanced to produce substantially pure yellow when the state comes exact to FIG. 30C. Further, as the state shifts from FIG. 30C to FIG. 30D, the ratio of red included in green gradually decreases, changing the substantially pure yellow to gradually wear a greenish hue and eventually be infinitely close to green.
The duration time of the state of FIG. 30C in the transboundary state, i.e., the duration time of the color mixing increases in proportion to the diameter of the spotlight 3, i.e., an angle α at which the left and right external tangents 4 and 5 of the spotlight 3 shown in FIG. 30D cross each other at the rotational center of the color wheel 1. For example, in a case where the angle α is 30 degrees, the color mixing (for example, red→yellow→green) continues while the spotlight 3 is irradiated on the ranges of 15 degrees ahead and rear of the boundary 4 between the two areas, i.e., the range of the angle α (=30 degrees).
FIGS. 31A to 31F are timing charts showing the timings to drive the color wheel of the conventional apparatus. In FIGS. 31B to 31E, the R image, the G image, the B image, and the W image are image signals supplied, as time-divided, to a light modulation device (see a later-described DMD 34: FIG. 2). The R image is an image signal of R components extracted from a frame image of RGB, the G image is an image signal of G components extracted from the same frame image, the B image is an image signal of B components extracted from the same frame image, and the W image is an image signal for an image to be displayed fully white (a luminance image as an image signal comprising only luminance information may replace the W image).
A color image can be displayed on a screen by sequentially supplying the R image, the G image, the B image, and the W image to the light modulation device in synchronization with the rotational positions (the respective positions of the R area 1a, the G area 1b, the B area 1c, and the W area 1d) of the color wheel 1 as shown in FIG. 31, and irradiating a light flux made up of the red, green, blue, and white modulated lights as modulated according to these images onto the screen from the projection display apparatus.
Here, the projection display apparatus has two typical use styles: one that puts a high value on the color reproductivity such as for home theater, and the other where the brightness is important such as for presentation. In the case where the color reproductivity is highly valued, the color purity of the R area 1a, the G area 1b, and the B area 1c of the color wheel 1 may be increased, so that each color may be as close to the primary color as possible. However, this in turn decreases the light transmissivity, and the brightness cannot be secured. Thus, the presentation use cannot be satisfied in this case. Contrarily, if the transmissivity of the R area 1a, the G area 1b, and the B area 1c of the color wheel 1 is increased or the transmissivity of the color wheel 1 as a whole is increased by preparing the W area or in other manners in order to obtain a sufficient brightness, the color purity is lost and the home theater use thus cannot be fulfilled. The brightness can also be secured by increasing the amount of light from the light source, but this entails a limit in terms of heat generation and power consumption.
As demanded by these backgrounds, the illustrated conventional apparatus is made capable of varying the drive time of the W image (or the luminance image). That is, as shown by an arrow T in FIG. 31E, the drive time of the W image is increased for securing the brightness, while the drive time of the W image is shortened for securing the color reproductivity, so that the above-described two uses are both met.
The prior art fails to explain the period during which the spotlight 3 crosses the boundary 4 between two areas (the period of the above-described transboundary state), i.e., the period of the 15 degree (α/2) ranges prior and posterior to the spotlight 3 crossing the boundary between the R area 1a and the G area 1b and the boundary between the G area 1b and the B area 1c. If the W image is driven during this period, it can be considered that the brightness can further be increased.
FIGS. 32A to 32C are timing charts showing the timings to drive the color wheel in a case where the W image is driven also in the transboundary state. As shown in FIGS. 32A to 32C, the drive time of the W image includes not only the W area 1d of the color wheel 1 but also the 15-degree (=α/2) ranges at the front and the back of the boundaries between the areas, i.e., the 15-degree ranges at the front and the back of the boundary between the R area 1a and the G area 1b, the 15-degree ranges at the front and the back of the boundary between the G area 1b and the B area 1c, the 15-degree ranges at the front and the back of the boundary between the B area 1c and the W area 1d, and the 15-degree ranges at the front and the back of the boundary between the W area 1d and the R area 1a. The total drive time of the W image equals the angle of the W area 1d+3α=90 degrees+30 degrees+30 degrees+30 degrees, resulting in that the W image can be driven for as long a time as 180 degrees corresponding to about the half round of the color wheel 1, contributing to further increasing the brightness.
It is good for the above-described conventional apparatus if the white image is driven for such a long time as 180 degrees corresponding to about the half round of the color wheel 1, because the brightness can be further increased. However, on the other hand, since only W becomes prominently large, its balance with R, G, B, and their complementary colors (C, M, Y) is destroyed and the white portions will be heavily emphasized, giving rise to a problem that the colors in the projected image will be subdued.
FIGS. 33A and 33B are the CIE xy chromaticity diagram of the conventional apparatus, and a conceptual diagram of the brightness of each image. In the CIE xy chromaticity diagram, the vertices of the triangle represents the chromatic coordinates of red (R), green (G), and blue (B), likewise the foregoing CIE xy chromaticity diagram. C (cyan) is the complementary color of R, M (magenta) is the complementary color of G, and Y (yellow) is the complementary color of B.
When the respective images of R, G, B, C, M, Y, and W are compared in terms of brightness, it will roughly be a ratio of “R:G:B:C:M:Y:W=1:1:1:2:2:2:9” as shown in FIG. 33B. This is because the W image is driven for such a long time as 180 degrees corresponding to about the half round of the color wheel 1 as described above.
It is generally said that the proper ratio among R, G, B, C, M, Y, and W is about “1:1:1:2:2:2:3”, where R, G, and B with respect to C, M, and Y is about “1:2”, and R, G, and B with respect to W is about “1:3”. It is believed that an ideal balance between the color and the brightness can be achieved at this ratio. Thus, the ratio of the conventional apparatus greatly diverges from this balance, and the colors it produces therefore seem subdued.
As described above, the above-described conventional apparatus is effective in a point that the brightness can be increased, but has a problem that it cannot make subtle adjustments, for example, emphasizing a specific color, focusing on color shading, balancing color shade and color purity, or giving preference to color purity, etc., i.e., minute adjustments that relate to man's subjectivity.
Hence, an object of the present invention is to provide a projection display apparatus and a display control method thereof, which can flexibly adapt to a wide range of demands from brightness preference to color reproductivity preference, by making the driving pattern of the color wheel variously changeable with respect to each area and each image.